Tweaks to PPB_VarArrayBuffer in preperation for taking out of Dev.

ppapi/proxy/plugin_array_buffer_var.cc

Index: ppapi/proxy/plugin_array_buffer_var.cc
diff --git a/ppapi/proxy/plugin_array_buffer_var.cc b/ppapi/proxy/plugin_array_buffer_var.cc
index d88ca7bd3f96d627941ffd254ac8117650a4aac6..cc943ba72daa124b0c8253fc43de492edd36495b 100644
--- a/ppapi/proxy/plugin_array_buffer_var.cc
+++ b/ppapi/proxy/plugin_array_buffer_var.cc
@@ -23,6 +23,10 @@ void* PluginArrayBufferVar::Map() {
   return &(buffer_[0]);
 }
 
+void PluginArrayBufferVar::Unmap() {
+  // We don't actually use shared memory yet, so do nothing.
+}
+
 uint32 PluginArrayBufferVar::ByteLength() {
   return buffer_.size();
 }